This white paper describes the distinction between failure rate prediction and estimation methods in general and then gives an overview of the procedures used to obtain dangerous failure rates for certain mechanical equipment using exida FMEDA predictions and OREDA estimations. exida frequently compares field failure rate data from various sources to FMEDA results in order to validate the FMEDA component library. However, because OREDA and FMEDA methods are quite different, it is not possible to compare their results directly. A methodology is presented which creates predictions and estimations that are more comparable. The methodology is then applied to specific equipment combinations and the results are compared. When differences in the results exist between the two methods, plausible explanations for the differences are provided.
The comparisons show that the OREDA failure rates are well within the range of the exida FMEDA results. The comparisons also show that, with two exceptions, the average FMEDA predictions for dangerous failure rates are only slightly less than those of the OREDA estimations. In those two exceptions, FMEDA predictions are higher than OREDA. Therefore, it is reasonable to conclude that, when compared in an “apples-to-apples” fashion, for the equipment analyzed in this paper, the exida FMEDA predictions and OREDA estimations are quite comparable.